Mixer circuit for electronic musical instrument providing staircase tone signal

ABSTRACT

Disclosed is a tone generator circuit for use in an electronic musical instrument, in which respective output terminals of a plurality of cascaded flip-flop circuits are connected to control electrodes of active elements such as transistors, said active elements are adapted to effect a switching action with their predetermined on-state resistances in response to magnitudes of signal potentials applied to the control electrodes from the outputs of the flip-flop circuits, other electrodes of the elements are connected as groups at common connection points at each of which a load means is connected, and in each said group of the active elements, a signal is derived across the load means in the form of summed potentials from the commonly connected other electrodes, whereby tone signals each having a sawtoothapproximating staircase wave and a different fundamental frequency are provided. The tone generator circuit minimizes the use of passive elements such as capacitors and resistors, etc. and thus allows it to be constituted only by active elements without using many passive elements and therefore, an integration of the circuit is facilitated. Further, said active elements function to reduce the loads of said flip-flop stages and provide buffer effects between said stages, to insure reliability in the operations of the tone generator circuit.

United States Patent Yasujl Uchiyama [72] Inventor 3,534,144 10/1970 Ring 84/1 .01 Hamakita,Japan 3,478,633 11/1969 Mallett 84/1.03 [21] Appl. No. 38,795 3,538,806 1l/l970 Bunger 84/l.l2 [22] Filed May 19, 1970 W, izzzzzzsrxz'zzz' izss;mm, [73] Assign gz zr fgtf i fg fi Kaisha Anorney-Cushman, Darby & Cushman 9 [32] Priorities May 21, 1969 'P ABSTRACT: Disclosed is atone generator circuit for use in an [3]] B9379; electronic musical instrument, in which respective output ter- May 1969 Japan 44/39380 minals of a plurality of cascaded flip-flop circuits are connected to control electrodes of active elements such as transistors, said active elements are adapted to effect a [54] MIXER CIRCUIT FOR ELECTRONIC MUSICAL switchlng action with their predetermined on-state resistances gggig PROVIDING STAIRCASE TONE in response to magnitudes of signal potentials applied to the 7 Claims 70.1""! F control electrodes from the outputs of the flip-flop circuits, g other electrodes of the elements are connected as groups at [52] US. Cl 84/l.23, common connection points at each of which a load means is 84/DIG. 11, 307/223, 328/14 connected, and in each said group of the active elements, a [51] Int. Cl i G10h 5/06 signal is derived across the load means in the form of summed [50] Field of Search 84/1.01, potentials from the commonly connected other electrodes, 1.03, 1.22, DIG. 11, 1.11, 1.19, 1.23; 307/223 R, whereby tone signals each having a sawtooth-approximating 227; 328/ 14, 43, 186 staircase wave and a different fundamental fre uency are roi q P I vided. The tone generator circuit minimizes the use of passive References cued elements such as capacitors and resistors, etc. and thus allows UNITED STATES PATENTS it to be constituted only by active elements without using 3,430,073 2/1969 Leonard 307/223 X many passive elements and therefore, an integration of the cir- 3500213 3/1970 Ameauw 328/14 cuit is facilitated. Further, said active elements function to 3,535,969 10/1970 Bunger 84/1 l reduce the loads of said flip-flop stages and provide buffer ef- 3,577,084 5/1971 Atcherson et al 328/14 fects between said stages, to insure reliability in the operations 3,535,429 10/1970 Uchiyama 84/1.01 wne senerawrcircuit F F3 F4 2 men l u m) t z(2f1 tam l v 1 l n r 1 MASTER FLIP FLIP FLIP FLIP a- OSCILLATOR FLOP FLOP FLOP FLOP I l 1 1 I l a l' a r e R Qs Q4 1 P RI 2 R0 1, b

Ansmr n on: V1 I971 sum 2 OF 4 I I I I F3 F4 f" a um -t 2(2f) g t a(f) q l [I 11 IT MASTER FLIP- FLIP FLIP FLIP OSCILLATOR FLOP FLOP FLOP FLOP I Q .1 l l H G Y Q2 v Q3 Q4 Ro I R0 f I c Tb F I F2 F3 F4- F O(l6fI t|(8f) tz;(4f) t (2f I um A L 1 L K I I I L I I I I I MASTER FLI P FLIP 1 FLIP 6, FLIP HI. FLIP OSCILLATOR FLOP FLOP FLOP FLOP FLOP FIG. 4 7 "I W 7 Q2 Q3 Q4 '05 Q \R \P 7 R0? 7 R I Va *Tu y Th F lUuEUfDIZ X93017 uamynm PATENTEU DEC 7 I971 SHEET 3 or 4 -Va v I FLIP MASTER OSCILLATOR F FIG. 5

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mm!) x MIXER CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT PROVIDING STAIRCASE TONE SIGNAL BACKGROUND OF THE INVENTION The present invention relates to a tone generator circuit for use in an electronic musical instrument, and more particularly to a tone generator circuit capable of easily providing a sawtooth-approximating staircase wave signal and suitable for an integrated circuit construction.

As a tone source in an electronic musical instrument, a sawtooth wave signal including a fundamental component and all harmonic components with the level rates proportional to the reciprocals of the harmonics orders has been preferred. In the prior art, such a sawtooth wave signal having a suitable frequency spectrum as described above, in one example, involves a rectangular wave signal produced by circuits such as flip-flop circuits which rectangular wave is differentiated to be converted into a pulse wave signal, either of the positive-going and negative-going pulses of the wave signal is derived, and then the desired pulse wave is integrated, thus providing a desired sawtooth wave signal. However, the amplitude of this produced sawtooth wave signal has become considerably smaller than that of the input rectangular wave signal and hence, this type of prior art sawtooth wave signal needs to be amplified to a predetermined amplitude by employing amplifier circuits. As a result, many difficulties have been encountered in providing sawtooth wave signals having the predetermined amplitude in constitution and production costs since the number of the required signals is equal to that of tones provided in the electronic musical instrument. Furthermore, a differentiating circuit and 'a integrating circuit employed for forming such a sawtooth wave signal in a conventional tone generator circuit both include a number of capacitors and resistors, so that an integration of a tone generator circuit of this type can hardly be made, and as a matter of fact, such circuit integration has been impossible. In another example of the prior art, there is a system of tone generators in which a plurality of flip-flop circuits are used to produce octavely related square waves and mixing circuits having resistors are provided to mix the produced square waves. The system, however, is disadvantageous in that the square waves are mixed through appreciably large resistances to prevent the interactions between the flip-flop circuits, so that no increased output signal is obtained, the provision of heavy loads causes instability in operations of the system, and the use of the large resistances has made an integration of the system difficult.

SUMMARY OF THE INVENTION One object of the present invention is to provide a tone generator circuit for use in an electronic musical instrument, simply providing a desired tone signal of a sawtooth-approximating staircase wave which is suitable for practical use.

Another object of the present invention is to provide a tone generator circuit in which the use of passive elements such as capacitors and resistors and the number of constituent components of the circuit are minimized.

A further object of the present invention is to provide a tone generator circuit of a simple structure almost consisting of active elements such as F ETs and suitable for an integrated circuit.

tone generator circuit capable of being easily manufactured in mass production, and which is not expensive but stable in operation.

The present invention is based on the recognition that a A still further object of the present invention is to provide a sawtooth-approximating staircase wave having not all harmonic components is satisfactorily useful or practical as a tone signal for an electronic musical instrument.

According to one embodiment of the present invention, there is provided a tone generator circuit in an electronic musical instrument comprising a plurality of flip-flop circuits each having its output terminal developing an octavely related square wave, a plurality of active elements such as field effect F ETs being connected in common as groups, and load means connected individually to each common connection point between said drains and across each of which variations in drain potentials of the FETs are added and derived in each said group, whereby a tone signal consisting of a sawtooth-approximating staircase wave of a large amplitude and a different fundamental frequency is obtained at each of said load means. This circuit does not need any of differentiating circuits and integrating circuit as required in the conventional circuit, resulting in reduction of the production cost and eliminates a trouble in operation due to the interaction between the outputs of the flip-flop circuits, by buffer effects of said active elements.

Other objects, features and advantages of the present invention will be well understood from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing one embodiment of a tone generator circuit using transistors therein in accordance with the present invention,

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIGS. 3 through 5 respectively are circuit diagrams showing further embodiments of the present invention, using therein F ET's.

FIGS. 6 and 7 are diagrams for illustrating the operations of the circuits shown in FIGS. 1 and 3 and FIGS. 2 and 4, respectively,

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, similar characters represent similar parts.

Referring to FIG. I, there is shown a tone generator circuit arrangement according to one embodiment of the present invention, in which a frequency divider circuit consisting of a multiplicity of cascaded flip-flop circuits F F F F (here four flip-flop circuits are shown for the purpose of illustration) is provided, the input of a first flip-flop circuit F of the divider circuit is connected through a clipper circuit (not shown) to a master oscillator O of an electronic musical instrument generating a sine wave output signal and is adapted to receive a square wave converted from said sine wave by the clipper circuit, and output terminals t, I of the flip-flop circuits F F and F are connected through separate resistors r with the bases of transistors Q, Q and Q and 0, respectively, whose emitters are connected in common at a point e grounded through a resistor R and a capacitor C connected in parallel.

Between the collectors of each group of transistors Q and Q and transistors 0 and Q, is connected a series circuit of resistors R and R individually. At connection points P,, and P,, of said each group between the resistors R and R respective one ends of load resistors R are connected thereto and they are connected to a power supply voltage +V, The connection points P and P respectively are connected to tone signal output terminals T and T,,

Now, description is made to the operation of the abovedescribed circuit arrangement.

As is well known, an output signal of the master oscillator O, which is a sine wave with a predetermined frequency of 8f Hz., is converted into a square wave of the same frequency in the clipper circuit, and when the square wave is supplied to the input of the flip-flop circuit F,, at the terminals r t and 2;, square wave signals respectively having frequencies of 4f, 2f and l f Hz. are established, respectively.

Now, assume that the square waves derived at the output terminals 1 and of the flip-flop circuits F and F are waveforms shown in FIGS. 6( I) and 6(ll) respectively, and resistors R,, R and R have the following relations:

R,=2R R,, R,, R

The output potential waveform at the output terminal T,, becomes a sawtooth-approximating staircase wave as shown in FIG. 6(III). That is, the conducting period of time of transistor Q, is a period of d, and d, as shown in FIG. 6(I), while the conducting period of time of transistor Q, is a period of d, through d, as shown in FIG. 6(II). Therefore, assuming that collectoremitter impedances at the conducting state of transistors Q, and Q and the resistance of common emitter grounded resistor R are negligible, direct current potentials V,, V V and V, of the output terminals T, with respect to said respective times d,, d d, and d vary as indicated by the following formulas:

The relation V, V V,, V. is obtained. Then, if the above condition, R,=2R R,, R,, R is taken, the above formulas (l), (2),(3)become:

Therefore, it will be seen that an output signal or a tone signal of a staircase wave witha frequency of 2f Hz. whose each step is an equal potential as shown in FIG. 6(III) is obtained at the output terminal T,,.

However, if R,, is too small as compared with R, and R the staircase wave tone signal will become too small in amplitude. Practically, even if R,=2R and R,, 2R,, for example, R,= 4K0, R =2KQand R,,=IKO, a desired waveform tone signal may be obtained.

Also, at the output terminal T,,, a staircase wave tone signal having each step being the same potential with a repetition frequency offHz. may be derived.

Now, reference is made to another embodiment of the present invention as shown in FIG. 2. A master oscillator O generating a sinusoidal wave is connected through a clipper circuit to cascaded flip-flop circuits F, to F, to the input of which a square wave signal is supplied, and thus, the cascaded circuits constitute a frequency-dividing circuit. An output terminal of the flip-flop circuit F, is connected through a resistor r to the base of a transistor 0,, output terminals t and t, of the flip-flop circuits F and F respectively are connected through separate resistors r to the bases of transistors 0 and Q, and the bases of transistors 0 and Q and an output terminal 1., of the flip-flop circuit F is connected through another resistor r to the base of transistor Q,,, the collectors of transistors 0,, Q and Q, as well as the collectors of transistors 0,, Q, and Q, are connected respectively via resistors R,, R and R to common connection points P, and P, which points are connected to tone signal output terminals T,, and T respectively, and are connected through individual load resistors R, at a power source voltage +V,.

The emitters of said transistors Q, to Q are connected at a common connection point e, which point is grounded via a parallel circuit of a resistor R and a capacitor C.

Description will be made of the operation of the abovedescribed tone generator circuit.

With a square wave signal having a repetition frequency of 16f Hz. applied to the flip-flop circuit F,, four kinds of square waves having frequencies of 8f, 4f, 2f and f Hz. are developed at the output terminals t,, t and respectively. Now, supposing that the waveforms of the square wave signals derived at the output terminals t,, t, and of the flip-flop circuits F,, F, and F are as shown in FIGS. 7(l), 7(ll), 7(III) and the relations between the resistances of said resistors R,,, R,, R and R are as R,=2R =4R,,, and R,, R,, R R at the output terminal T, provided is a tone signal of a staircase waveform with a frequency of 2f Hz., whose each step has an equal potential, as shown by enlarged waveforms in FIG. 7(III). The staircase waveform approximates a sawtooth wave considerably more than the waveform shown in FIG. 6(III) does. Practically, even when the resistors R and K, have the relation of R,, R for example, resistors R,, R,, R, and R take 8K0, 4K9, 2K0 and (0, respectively, a satisfactory sawtooth-approximating staircase wave signal may be provided in such a circuit arrangement.

Also, at the output terminal T,,, such a sawtooth-approximating staircase wave tone signal may be provided as similarly as described above. Then the produced signal has a repetition frequency of f I-Iz.

Referring to FIG. 3 there is shown an embodiment of a tone generator circuit in accordance to the present invention, employing FETs in the circuit shown in FIG. 1 in place of transistors of the type which has a base, emitter and collector, in which the respective gates, drains and sources of FETs Q,,, Q,,, Q, and 0,, may be used in the circuit wiring of FIG. 1 to correspond to the respective bases, collectors and emitters of transistors 0,, 0,, Q, and 0,. At that time, the output terminals l,, 1 and 1;, of the flip-flop circuits may be connected to the gates of the FETs Q,,, Q, Q, and 0,, in the manner shown in FIG. 3. The resistors r used in the arrangement of FIG. I may be omitted in this embodiment, so that the number of the circuit components is advantageously reduced. The use of FETs of the N-channel enhancement mode or the P-channel enhancement mode pennits the source of each FET to be directly grounded. In the abovementioned construction of the circuit, tone signals of sawtooth-approximating staircase waves whose each step has an equal potential with frequencies of 2f and f Hz. are also developed at the output terminals T,, and T respectively, as shown in FIG. 6(III).

By taking the on-state source-drain resistances of the F ETs Q, and Q, and the F ETs Q and 0., equal to the resistances of R, and R, respectively, the operations of the circuit of this embodiment will become similar to those in the first embodiment of the present invention.

Referring to FIG. 4, there is shown another embodiment in which in the circuit illustrated in FIG. 2, transistors 0, through 0,, are replaced with FETs. In the circuit arrangement of FIG. 4, at each of the output terminals T, and T a tone signal of sawtooth-approximating staircase wave with its each step having an equal potential as indicated in FIG. 7(IV) may be provided.

It is of course understood that the use of silicon transistors to the circuits using the transistors Q, through Q permits that the common emitter connection point e is directly grounded.

In a modification of the circuit arrangements shown in FIGS. 2 and 4, a number of octavely related square waves derived at respective output terminals of a multiplicity of cascaded flip-flop circuits are added through individual transistors of an ordinary type or FETs, so that a tone signal of a sawtooth-approximating staircase wave having steps still more than those in the staircase waveform shown in FIG. 7(IV) may be provided.

Further, in the embodiment illustrated in FIG. 3, FETs are applicable as a substitution of load resistors R,,. Such a modified tone generator circuit is shown in FIG. 5, which comprises FETs Q, as load means, having their sources connected to the common connection points P and P,,, respectively, and their gates and drains connected to the power source voltage V,. When as the FETs Q, to Q an Q to 0,, in the above-mentioned embodiments, FET's of a junction type or a depletion mode may be used, the common connecting points of said FETs Q to Q and 0,, to 0,, are grounded via a parallel circuit consisting of a resistor having a low resistance and a capacitor having a large capacity to provide a suitable DC biasing potential.

In FIGS. 3 and 4 the embodiments are illustrated in which N-charmel enhancement mode FET's are employed as FETs Q, to Q,,, but the use of P-channel enhancement mode FETs in place of the N-channel enhancement mode FETs, much facilitates integration of the circuit together with P-channel enhancement FETs employed. in the flip-flop circuits, thus permitting an easy integration of a tone generator circuit for use in an electronic musical instrument.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

l. A mixing circuit in an electronic musical instrument for synthesizing a staircase-shaped tone signal, said mixing circuit comprising: 7

a plurality of flip-flop circuits connected in cascade as a frequency-dividing circuit and having output terminals for providing harmonically related square wave outputs,

at least one group of active elements, each active element having first and second electrodes and a control electrode,

said control electrodes being connected to respective output terminals of said flip-flop circuits whereby the corresponding active element rendered conductive or nonconductive in response to'electrical potential variations in signals from said output terminals,

said first electrodes all being connected in common to a proper potential operating point;

a plurality of resistance, each resistance being associated with a corresponding active element and effectively individually connected at one end to the second electrode thereof, and

a common load means provided for each said group and connected in common to the other ends of said resistance associated with said active elements included in that group for effectively mixing signals therefrom;

said resistance having values individually determined to cause the mixing ratios of the signals to be mixed in each group to produce a mixed resultant signal of a staircaseshaped waveform having equal step intervals.

2. A mixing circuit as in claim 1, wherein each said common load means comprise properly gate-biased field effect transistors, each source electrode and each drain electrode thereof constituting two terminals of the respective common load means.

3. A mixing circuit as in claim 1, wherein said active elements are transistors, said first electrode is an emitter electrode, said second electrode is a collector electrode, and said control electrode is a base electrode,

4. A mixing circuit as in claim 3, wherein each of said resistances comprises an individual resistor and wherein said common load means comprises a resistor which is connected in common at one end to said other ends of the individual resistors and which is connected at its other end to a source of operating potential.

5. A mixing circuit as in claim 4, wherein each succeeding individual resistor of a group has a resistance value substantially equal to one-half of the resistance value of the individual resistor associated with the just preceding transistor and wherein the resistance value of said common load is less than the resistance value of the smallest said individual resistor connected thereto.

6. A tone generator in an electronic musical instrument including a mixing circuit asin claim 5 and further comprising a master oscillator for driving the cascade-connected flip-flop circuits and an output terminal connected to said one end of each common load means for providing the desired staircaseshaped waveform with equal step intervals.

7. A mixing circuit in an electronic musical instrument, said circuit comprising:

a plurality of flip-flop circuits connected in cascade as a frequency-dividing circuit and having output terminals for providing harmonically related square wave outputs,

at least one group of field effect transistors, each transistor having a source electrode, a drain electrode and a gate electrode,

said gate electrodes being connected to respective output terminals of said flip-flop circuits whereby the corresponding transistor is rendered conductive or nonconductive in response to electrical potential variations in signals from said output terminals,

said source electrodes being connected in common to a proper potential operating point;

common load means provided for each said group and connected in common to all of said drain electrodes of the field effect transistors in that group for mixing signals therefrom;

said field effect transistors having on-state source drain resistance values respectively proportioned to cause the mixing ratios of the signals to be mixed in each group to produce a waveform shape having equal step intervals. 

1. A mixing circuit in an electronic musical instrument for synthesizing a staircase-shaped tone signal, said mixing circuit comprising: a plurality of flip-flop circuits connected in cascade as a frequency-dividing circuit and having output terminals for providing harmonically related square wave outputs, at least one group of active elements, each active element having first and second electrodes and a control electrode, said control electrodes being connected to respective output terminals of said flip-flop circuits whereby the corresponding active element rendered conductive or nonconductive in response to electrical potential variations in signals from said output terminals, said first electrodes all being connected in common to a proper potential operating point; a plurality of resistance, each resistance being associated with a corresponding active element and effectively individually connected at one end to the second electrode thereof, and a common load means provided for each said group and connected in common to the other ends of said resistance associated with said active elements included in that group for effectively mixing signals therefrom; said resistance having values individually determined to cause the mixing ratios of the signals to be mixed in each group to produce a mixed resultant signal of a staircase-shaped waveform having equal step intervals.
 2. A mixing circuit as in claim 1, wherein each said common load means comprise properly gate-biased field effect transistors, each source electrode and each drain electrode thereof constituting two terminals of the respective common load means.
 3. A mixing circuit as in claim 1, wherein said active elements are transistors, said first electrode is an emitter electrode, said second electrode is a collector electrode, and said control electrode is a base electrode,
 4. A mixing circuit as in claim 3, wherein each of said resistances comprises an individual resistor and wherein said common load means comprises a resistor which is connected in common at one end to said other ends of the individual resistors and which is connected at its other end to a source of operating potential.
 5. A mixing circuit as in claim 4, wherein each succeeding individual resistor of a group has a resistance value substantially equal to one-half of the resistance value of the individual resistor associated with the just preceeding transistor and wherein the resistance value of said common load is less than the resistance value of the smallest said individual Resistor connected thereto.
 6. A tone generator in an electronic musical instrument including a mixing circuit as in claim 5 and further comprising a master oscillator for driving the cascade-connected flip-flop circuits and an output terminal connected to said one end of each common load means for providing the desired staircase-shaped waveform with equal step intervals.
 7. A mixing circuit in an electronic musical instrument, said circuit comprising: a plurality of flip-flop circuits connected in cascase as a frequency-dividing circuit and having output terminals for providing harmonically related square wave outputs, at least one group of field effect transistors, each transistor having a source electrode, a drain electrode and a gate electrode, said gate electrodes being connected to respective output terminals of said flip-flop circuits whereby the corresponding transistor is rendered conductive or nonconductive in response to electrical potential variations in signals from said output terminals, said source electrodes being connected in common to a proper potential operating point; common load means provided for each said group and connected in common to all of said drain electrodes of the field effect transistors in that group for mixing signals therefrom; said field effect transistors having on-state source drain resistance values respectively proportioned to cause the mixing ratios of the signals to be mixed in each group to produce a waveform shape having equal step intervals. 